Deflection system for a flat tube display



arch 1969 s. E. HAVN ET AL.

DEFLECTION SYSTEM FOR A FLAT TUBE DISPLAY Sheet Filed March 27, 1967 FIG.|.

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United States Patent Ofiice 3,435,277 Patented Mar. 25, 1969 3,435,277 DEFLECTION SYSTEM FOR A FLAT TUBE DISPLAY Svend E. Havn, Liverpool, and Mooshi R. Namordi, North Syracuse, N.Y., assignors to General Electric Company, a corporation of New York Filed Mar. 27, 1967, Ser. No. 626,272 Int. Cl. H01j 29/70 US. Cl. 315-18 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to an image display system, and more particularly, to electron beam deflection arrangements for relatively shallow cathode ray tubes.

An image display system, of the type in which this invention has application, is shown and described in U.S. Patent No. 3,177,395, which is assigned to the assignee of the present invention. In such a system, a shallow cathode ray tube is employed having a target area positioned on a display or viewing wall of the tube and having a vertical deflection means spaced from the target area on an opposite Wall of the tube. Suitable operating potentials are applied to the target area and to the deflection means for providing a potential gradient therebetween such that, when an electron beam which is directed into the space separating the target area and the deflection means, the beam is deflected from one extremity of the target to an opposite extremity of the target.

Horizontal deflection is accomplished by entry of the electron beam into a space between the target area and the first-mentioned deflection means and resolution into a plurality of spaced parallel paths which are substantially parallel to the target area. It is to be understood that the terms horizontal and vertical deflection are used in a relative sense, for convenience, to denote two mutually perpendicular directions of scanning.

In a prior art apparatus of this type, the vertical deflection was achieved by an excursion of a vertical sweep voltage which was of a relatively high magnitude and was normally well in excess of a few thousand volts. While low power, static or constant potential, voltages in the order of a few thousand volts may be supplied by relatively inexpensive and well-known circuits, a controlled sweep voltage having excursions in this order of magnitude heretofore required may be economically generated only by resorting to techniques approaching a commercially prohibitive expense. Furthermore, the state-of-theart vertical sweep voltage systems render the utilization of semiconductor circuits unrealistic in certain circumstances. Therefore, it is desirable to minimize the required excursion of the vertical deflection voltage to overcome the obstacles in the design of the generator for the vertical deflection voltage.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a shallow cathode ray tube having an increased sensitivity to a vertical deflection voltage.

It is another object of this invention to provide an improved shallow cathode ray tube in which vertical scanning is effected with a vertical deflection voltage having a lesser peak-to-peak amplitude than presently known shallow cathode ray tubes.

It is a further object of this invention to provide a shallow cathode ray tube having increased sensitivity to a vertical deflection voltage without increasing the external dimensions of the tube.

Briefly, in accordance with one form of this invention, we provide a shallow cathode ray tube including a throat at the entrance to a target area which is reduced in size and offset from the axis of an electron source and funneling means producing a collimated electron beam. The funneling means is positioned so that the axis passes along the edge of the throat opposite the target area thereby allowing the collimated beam to be deflected toward the target area without obstruction while passing through the throat. Hence, the throat may be reduced to provide a greater voltage gradient for any given voltage sweep applied to electrodes positioned on two sides of the throat and yet avoid the striking of the electrodes by the electron.

In accordance with another form of this invention, the throat and electrodes mounted therein may be inclined toward the target area to obtain an even smaller throat dimension and still avoid contact between the electron beam and the throat electrode adjacent the target area. Thus, the sensitivity of the tube to deflection voltages is greatly increased.

BRIEF DESCRIPTION OF THE DRAWINGS The specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention. The invention may also be understood from the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a front view of a shallow cathode ray tube;

FIGURE 2 is an external bottom view of FIGURE 1;

FIGURE 3 is a side view of FIGURE 1 at section AA, illustrating an embodiment of the invention;

FIGURE 4 is a side view similar to FIGURE 3, illustrating another embodiment of the invention; and

FIGURE 5 is a side view similar to FIGURE 3, illustrating still another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS By way of explanation, a specific shallow cathode ray tube is illustrated in FIGURES 1 and 2 in which the deflection system of this invention may be embodied. The tube as shown in FIGURE 1 is subdivided diagrammatically into three portions which are designated by a first bracket I, indicating the image section, a second bracket VD, indicating the vertical deflection section, and a third bracket HD indicating the horizontal deflection and collimating section.

As seen in both FIGURES 1 and 2, a source of electrons, in the form of an electron gun 2, projects a beam of electrons 3 into a display area. A magnetic field is established between pole plates 4 which accomplish horizontal deflection in a Well-known manner utilizing a yoke 6, a deflection coil 8., and a source 10 of horizontal deflection signals. The magnetic field produced thereby deflects the beam in a plane parallel to the paper from a first extreme position 3 to a second extreme position 3". Magnetic pole plates 12 for collimating the electron beam are mounted adjacent the outside wall of the horizontal deflection section HD. Of course, various types of horizontal deflection sections may be used. The one that is the subject matter of the US. patent application Ser. No. 141,-

863, filed Sept. 29, 1961, now abandoned, by Svend E. Havn which is assigned to the assignee of the present invention is an example of one such section. In the horizontal deflection section HD, the pole plates 12 are joined at the right hand ends by a magnet 14 and are so shaped that the beam of electrons emerges along parallel vertical paths lying in substantially the same plane. The horizontally scanned beam thus formed enters the throat of the vertical deflection section VD and emerges into a space therefrom to scan a target 16.

Various types of image sections may be used, as for instance the one that is the subject matter of US. Patent No. 3,155,872, which is assigned to the assignee of the present invention. The image section of the shallow cathode ray tube illustrated in FIGURES 3-5 is in substantial conformity with the teaching of the above-mentioned patent. The tube envelope is shown as made of glass, though other suitable materials may comprise various portions or all of the tube envelope. In the following discussion, the term resistive means refers to a means having suflicient resistance so as not to unduly load any source of voltage applied across it, and the term conductive coating, lining, or strip refers to means which have an insignificant amount of voltage difference between any two points thereof.

Referring now to the embodiment of the invention disclosed in FIGURE 3, the target 16 may comprise a customary phosphor layer 18 deposited on the inside of the front wall of glass and an aluminum or other electron permeable metallic coating 20 deposited on its inside surface. A resistive coating 24 is formed on the back wall and extends downwardly until it makes an electrical connection 27 with a conductive lining 26 extending along the back wall into the vertical deflection section VD forming an extended portion of a first electrode and terminating in the throat thereof. The conductive lining 26 is a means for applying deflection voltage signals from a source 32 to the resistive coating 24 and a means for deflecting the beam on to the target 16. A conductor 28 makes electrical contact with the resistive coating 22 and 24 all along the intersection at the top right corner to establish a deflection potential. In the particular embodiment of the invention shown, one portion of the throat is defined by a conductive strip forming another portion of the first electrode which is electrically connected to the conductive lining 26. The strip 25 is mounted or deposited on a protrusion 35 in the wall of the shallow cathode ray tube and inclined toward the target 16 thereby defining one side of a throat of reduced cross-section.

Similarly, the opposite side of the throat is defined by a conductive coating 23 including a portion extending toward the target 16 and forming a second vertical deflection electrode. The coating 23 is deposited on the wall 36 of the shallow cathode ray tube and is inclined toward the target 16. The throat thus formed has a gap of width W centered upon a throat axis X -X which is inclined with respect to the center line of an electron beam tunneling means comprising the conductive coating 13 and with respect to the beam 3. Hence, it may be seen that the gap width W of the throat, as defined by the conductive strip 25 and the coating 23, is axially inclined and displaced with respect to the electron beam 3. This configuration allows the electron beam 3 to be deflected by a vertical sweep voltage of lesser magnitude since the electron beam 3 enters the throat adjacent the strip 25 so that deflection within the reduced gap Width W will not result in collision with the coating 23. Furthermore, the inclination of both the strip 25 provides a longer path through a reduced gap.

In addition, this embodiment achieves increased vertical deflection sensitivity by providing a conductive coating 21 electrically insulated from an extended portion of the coating 23 in the vertical deflection section VD of the tube opposite the lining 26 and the strip 25. The conductive coating 21 extends from the target 16 toward the throat of the vertical deflection section VD. Preferably, the coating 21 is an extension of a conductive coating 20 which is coextensive with the target 16. In such an event, an appropriate voltage may be supplied to both the coatings 20 and 21 through a lead 21 which extends through the glass envelope and makes electrical connection with the coating 21. Of course, the lead 21' would be equally effective if connected to the coating 20 with the connection being made at the top corner thereof. In order to provide a suitable operating potential for the conductive coating 23, which is lower than that established for the coating 21 to extend the transit time, a lead 23' may extend through the envelope and make electrical connections with the coating 23 as shown.

In other words, the coating 23 is maintained at a lower potential than the coating 21. The electrons therefore pass through the gap width W at a lower velocity than otherwise achieved allowing each electron to spend more time between the conductive coatings 21 and 23 and the deflection strips 25 and 26. This allows a voltage of lower amplitude to effect the necessary vertical deflection. The lower velocity of the electron beam therefore serves to supplement the increased vertical sensitivity achieved by the narrowing of the gap width W through displacement and inclination of the throat axis X -X with respect to the electron beam 3.

As may be seen, displacing and inclining the axis X X of the gap width W with respect to the axis of the electron gun 2 and the conductive coating 13 will allow the electron beam 3 to enter the gap width W in the throat of the shallow cathode ray tube at the right hand edge adjacent to the strip 25. Deflection within this narrow region will immediately incline the electron beam 3 and create the deflected beam path 31 which follows the contour of the inclined coating 21, while the undeflected beam path 33 will pass close to the strip 25 but not strike it Although the vertical sensitivity will be somewhat reduced the invention may be embodied in another form of a shallow cathode ray tube as shown in FIGURE 4 wherein the strip 26 is eliminated as well as the lead 23', and the coating 21 and the extended portion of the coating 23 are electrically connected to produce an equipotential surface supplied through the lead 21'. If the axis X X of the gap width W is displaced and inclined with respect to the axis of the electron gun 2 and the conductive coating 13 to establish an electron beam 3 aligned with the right hand edge thereof, the inclined surfaces of the strip 25 and the coating 23 will again allow a reduction of the gap width W to achieve increased vertical sensitivity since electrons deflected toward the target will not strike the displaced inclined coating 23.

The invention may also be embodied in a shallow cathode ray tube as shown in FIGURE 5 wherein the axis Y Y of a reduced gap width W is only displaced and not inclined with regard to the axes of the conductive coating 13 and the electron gun 2. The gap width W is defined by a strip 45 mounted on a protrusion 55, connected to the lining 26, and opposing a coating 43 including an extended portion mounted on a built-up corner '56 and connected to the lead 23'. The vertical sensitivity is enhanced by maintaining the coating 43 at a lower potential than the coating 21 and thereby increasing the transit time of the electrons through the vertical deflection section VD. A considerable reduction of the gap width W' may thus be achieved without creating a physical interference between the path 31 and the coating 43.

This invention is not limited to the use of any particular means for extending the transit time of the electrons through the vertical deflection electrodes; i.e., the strip 26, the coating 43, the coating 23, or the coating 21, nor is this invention limited to use with a particular shallow cathode ray tube as shown. Rather, the disclosed means for achieving a reduction in the gap width W or W between deflection electrodes may be utilized in various shallow cathode ray tube environments to effect an increased vertical sensitivity.

Although specific embodiments of the invention have been shown and described, it is not intended that the invention be limited to the particular form shown and described and it is intended by the appended claims to cover all modifications within the spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a shallow cathode ray tube system having an electron target, a horizontal deflection section disposed in spaced relationship opposite said target, a source of electrons for generating an electron beam generally parallel to said target, the improvement comprising:

(a) a vertical deflection section including a throat through which the beam passes prior to striking said target;

(b) said throat including a first deflection electrode and a second deflection electrode defining a gap at the entrance to said throat wherein the axis of the gap is displaced with respect to the electron beam produced by said source of electrons so that the electron beam incident upon the gap is nearer said first deflection electrode than said second deflection electrode, and

the target is nearer said second deflection electrode than said first deflection electrode.

2. The shallow cathode ray tube as recited in claim 1 wherein said second deflection electrode is inclined toward said target.

3. The shallow cathode ray tube of claim 2 wherein a first portion of said first deflection electrode is inclined toward said target.

4. The shallow cathode ray tube of claim 3 wherein said second deflection electrode includes an extended portion.

5. The shallow cathode ray tube of claim 4 wherein a second portion of said first deflection electrode is extended, is parallel to the electron beam, and is opposite said extended portion of said second deflection electrode.

6. The shallow cathode ray tube of claim 2 wherein a portion of said first deflection electrode is inclined toward said target.

References Cited UNITED STATES PATENTS 3/1959 Aiken 315-18 

